Downhole rotating jetting heads have been used to remove deposits from well tubular members. Fluid jetting heads driven by impulse motors, such as offset nozzles or turbines, tend to generate low drive torque. This makes the heads susceptible to stalling by deposit cuttings or by deposit bridges. Further, when the head stalls, no signal is given to surface that the head is not rotating. Further, jetting heads are most efficient when cleaning radially rather than axially, particularly for drilling through deposit bridges. Therefore, multiple runs into a well are often required to fully remove the deposits; first running a positive displacement motor (PDM) with a milling head to remove bridges followed by a run with a radial jetting tool to remove wall deposits.
U.S. Pat. No. 4,705,107 dated Nov. 10, 1987 shows a rotating cutting tool driven by a fluid turbine motor with fluid nozzles to assist in removing deposits from the tubular bore. However, spend fluid used for driving the turbine motor is utilized for the fluid nozzles and a flexible connection is provided between the cutting head and the fluid turbine motor which substantially limits the torque transmitted to the cutter. Further, no blades or cutting elements are provided on the lower end of the cutting tool for penetrating any bridge deposits.
It is desired that a milling head rigidly connected to the motor be provided with milling elements projecting downwardly from the lower end of the head along the axis of rotation for penetrating deposits bridging the tubular bore.
Further, it is desired that fluid jets be provided adjacent the upper end of the milling elements on the milling head to assist in the cleaning of the deposits from the tubular bore after milling with unspent power fluid being available for the fluid jets.